The embodiments described herein relate generally to steam turbines, and more particularly, to methods and systems for cooling turbine components of the steam turbine.
As steam turbines rely on higher steam temperatures to increase efficiency, steam turbines should be able to withstand the higher steam temperatures so as not to compromise the useful life of the turbine. During a typical turbine operation, steam flows from a steam source through an inlet in a housing to flow parallel to an axis of rotation along an annular hot steam path. Typically, turbine stages are disposed along the steam path such that the steam flows through vanes and blades of subsequent turbine stages. The turbine blades may be secured to a plurality of turbine wheels, with each turbine wheel being mounted to or integral to the rotor shaft for rotation therewith. Alternatively, the turbine blades may be secured into a drum type turbine rotor rather than individual wheels, with the drum integral with the shaft.
Conventionally, turbine blades may include an airfoil extending radially outwardly from a substantially planar platform and a root portion extending radially inwardly from the platform. The root portion may include a dovetail or other means to secure the blade to the turbine wheel of the turbine rotor. In general, during operation of the steam turbine, steam flows over and around the airfoil of the turbine blade, which is subject to high thermal stresses. These high thermal stresses may limit the service life of the turbine blades. Moreover, the blade root and adjacent rotor may experience high thermal temperatures and stresses from the steam flow. Conventional steam turbines may use blade and rotor body materials that are more temperature resistant. These temperature resistant materials, however, may increase the cost of the turbine blades.